Sound transmitting system



1937. E. KAMMER-ER 8,

SOUND TRANSMITTING SYSTEM Filed Aug. 3, 1935 AAAIAAAA v AAAAAAL v v INVENTOIR ERNST KAMMERER ATTORNEY Patented Nov. 9, 1937 PATENT OFFICE 2,098,392 SOUND mausmr'rmo SYSTEM Ernst Kammerer, Berlin-Tempelhof, Germany,

assignor to Klangfilm G. in. b. 11., Berlin, Germany, a corporation of Germany Application August 3, 1935, Serial No. 34.516

' In Germany July 14, 1934 3 Claims. '(01. ire-100.1)

In sound transmission equipment such as soun picture recorders orreproducers, it is desirable that the recorded or reproduced sound be checked by control means mounted at the sending end.

5 The apparatus most extensively used "for this purpose comprises a check-up or monitoring loudspeaker. The energy required for the monitor loudspeaker is usually derived from the amplifier feeding the main loudspeaker. It is known in this connection that the monitoring loudspeaker may be united with the same amplifier stage, either in parallel or in series relation to the main loudspeaker.

In the operation of such apparatus, however,

a number of difliculties arise. The monitoring loudspeaker is often mounted in a room having acoustic conditions or properties which are unfavorable 1 due to undesirable and disturbin noises. A situation like that prevails, for in-' stance, in the projector booths in sound-film theaters where the projector machines produce marked noises. Now, it has been found that in such places the monitor loudspeaker is difiicult' in low or subdued passages of the sound and that the secondary noises of the room mask it so that auditory (aural) check-up is under certain circumstances impossible or at all events unreliable.

Fundamentally speaking, it would, of course, be feasible to feed the monitor loudspeaker with more energy compared with the main loudspeaker so that it would turn out to be sufliciently loud during low passages; but this would be attended with the drawback that, on the one hand, the

' monitor loudspeaker would be unnecessarily loud 35 during loud passages and might fill a small transmitter room with sound almost to a point where thiswould be unbearable or uncomfortable, while, on the other hand, the energy of the main loudspeaker would be diminished to a point where the latter turns out to be too low.

The purpose of the present invention is to create an arrangement adapted and designed to render conditions so that the monitoring. loudspeaker, also during low or subdued passages will 45 be adequately loud even in rooms where there is a lot of noise,.while yet not causing unbearably large acoustic energies at loud passages. Incidentally the rendition of the sound by;-the main loudspeaker should not be diminished, while in 55 the plate circuit of the main loudspeaker power addition overmodulation of the tube feeding the factor exceeds that of the main loudspeaker tube.

In this instance, the monitoring loudspeaker tube could be modulated from the-amplifying stage whence also the main loudspeaker tube is con- 10 trolled.

In the case of using tubes of like gain for the main loudspeaker and the monitor, the. identical efiect is provided by coupling the tube'of the monitoring loudspeaker with the amplifier only 15 by the aid of such circuit means as will raise the amplification, for instance, the monitoringloudspeaker tube is connected with the amplifying loudspeaker stage which exercises a controlling action on the main tube byway of a step-up transformer. Instead of the latter circuit means insuring a corresponding efiect such as tubes con-, nected in suitable circuits may be used.

In the case of arrangements of this kind the danger of overmodulation of the monitoring loudspeaker tube is always very serious. Hence, according to a further object of this invention, distinct circtut means are provided for the coupling of the monitoring loudspeaker with a view to precluding over-modulation, the said protective means being preferably automatic in action,

and they may be designed to act as current or voltage limiters. In suitable circuit schemes; re-

- sistances may. be used therefor, the said resistances being of a nature so that by virtue thereof they will stabilize or practically stabilize the current. Resistances adapted for this purpose, such as iron-hydrogen resistances are known.

The invention will be better understood from the following description when considered in 40 connection with the accompanying drawing, and its scope will be pointed out in the appended claims. p

Referring to the drawing: I

Fig. 1 is a wiring diagram of an arrangement wherein the monitor speaker supply tube is energized from the plate circuit of the main speaker supply tube,

Figs. 2 and 3 are similar diagrams of modified arrangements wherein the main and monitor loud speakers are energized through parallel circuits, and f Fig. 4 illustratesa modified arrangement including means for preventing over-modulation oi the monitor speaker.

- 5 transformer l in known manner.

In the arrangement of Fig. 1, the input stage i is associated with the power tube of an ordinary amplifier by way of resistance and capacity. The main loudspeaker is connected.at 3 by way of a According to the invention, the plate circuit of the amplifier tube 2 contains another amplifier tube 5 which by way of the condenser. 6 is in coupling relationship with the tube 2, and which by the intermediary of the transformer 'I as known in the prior art, feeds a monitoring loudspeaker which is connected at 8. Below the power or end-stage tube 2 any desired number of amplifying stages may be provided- The power stage may consist also of two push-pull connected tubes. Instead of one monitoring loudspeaker 5 also several such devices could be provided.

monitoring loudspeaker may have any desired characteristic since it in no way controls the 20 operation of the main speaker.

Another embodiment of the invention is shown 1 in Fig. 2. Connected with the'input stage. I of a standard amplifier by way of resistance 9 and condenser I is the power tube H feeding the main lou peaker while, as known in the prior art, the mai loudspeaker is connected at l2. Connectedwith the same input stage I by way of capacity I3 is the power tube H feeding the monitoring loudspeaker, and with the same tube is joined at the monitoring loudspeaker. According to this invention, the gain of the tube ll of the monitoring loudspeaker is higher than that of the tube I l feeding the main loudspeaker. Fig. 3 illustrates another embodiment of the invention in which the power tube of the main loudspeaker and the monitoring loudspeaker may have the same relation as to amplification. Connected .with the input stage I by way of resistance 9,- capacity "I, as in Fig. 2, is the main loud- 40 speaker'tube II, and associated with the latter at l2, 'as known in the earlier art, is the main loudspeaker. The coupling of the monitoring loudspeaker tube I6 is effected by way of capacity i3 and the transformer I! provided according to this invention, the latter being so proportioned that it will stepup the voltage. The monitoring loudspeaker is connected at [5. a What happens as a result of the connection of input stage I The tube feeding the the transformer is that the amplification of tube I8 is raised to a value above that for tube II. For this purpose may be used also other suitable electric circuit means.

Fig. 4 shows a circuit preclude the'chances of overmodulation of the organization-designed to monitoring loudspeaker tube. Connected with the of a standard amplifier by way of resistance 9 and capacity I0, is the main loudspeaker power tube and with the latter, in turn, at I2 the main loudspeaker. In the plate circuit of the main loudspeaker tube H is included the monitoring loudspeaker tube It! with connection of the monitoring loudspeaker at IS. The coupling of the monitoring loudspeaker tube is eifected by way of the condenser 2 and a voltage divider comprising resistance parts 2| and 22. The resistance 2| is of the iron-hydrogen type designed to stabilize the current completely or I practically so with the result thatovermodulation of the tube will be avoided inasmuch as the control voltage is unable to exceed a definite value to be chosen in conformity with the modulation data of the tube.

In lieu of the iron-hydrogen resistor, a uranium lamp or the like may be employed. However, with a view to precluding over-modulation, recourse may be had also to other suitable amplitude-limiting means. Instead of one loudspeaker it is feasible to use a plurality of loudspeakers both for the main work as well as for monitoring.

Having now described my invention, I claim:

1. A sound-transmitting system including a main loudspeaker and a monitoring loudspeaker, an amplifier for actuating the main loudspeaker, a driving amplifier for actuating said first amplifier, and an amplifier having a higher gain than the first of said amplifiers connected to said driving amplifier for actuating said monitoring loudspeaker.

2. Apparatus as defined in claim 1 including means for preventing over-modulation of the amplifier actuating said monitoring loudspeaker.

3. Apparatus as defined in claim 1 including an iron-hydrogen resistor for preventing over-modulation of the amplifier actuating said monitoring loudspeaker.

, ERNST KAMMERER. 

